I'm not sure what your function is supposed to do.. but when you call it the way you do ("something = Round(test)") then the function also has to return a value of course... otherwise this function call wouldn't have any sense.
I edited your function, how it might work maybe, just try it.

I think the local x-variable should also be a float? And then it's returned... but however.
function Round(RoundX as float)
x as float
y as float
z as float
x = 45.49
y = int(x)
z = x - y
if z >= 0.5
x = ceil (x)
else
x = floor (x)
endif
endfunction x
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